The present invention relates to a semiconductor device and, in particular, to a semiconductor device having a vertical transistor.
Some semiconductor devices have vertical transistors. The vertical transistor is used, for example, in a device for controlling a high current. Some vertical transistors have a trench gate structure. The transistor having the trench gate structure has a structure in which a p-layer as a channel layer is formed over an n-layer as a drain and, further, an n-layer as a source is formed to the surface layer of the p-layer as shown, for example, in Japanese Unexamined Patent Application Publication No. 2000-353805 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-513518. The gate electrode of the trench structure extends from the p-layer to the n-layer. The lower end of the gate electrode enters in the n-layer.
Further, in Japanese Unexamined Patent Application Publication No. 2000-353805 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-513518, the n-layer as the source is disposed only on one lateral side of the trench gate. The p− region is formed to a depth more than the p well on the other lateral side of the trench gate. The p− region is disposed so as to lower the resistance of the drain region and ensure the withstand voltage of the transistor.